1. Field of the Invention
The present invention relates to apparatus and methods for restraining the heart. More particularly, the invention relates to apparatus and methods for accessing the pericardium and at least partially enclosing the heart with a cardiac restraint apparatus.
2. Description of the Related Art
The present invention is generally directed to apparatus and methods for restraint of the cardiac wall. The invention is particularly suited for the treatment of cardiac diseases which result in atrial or ventricular dilation. The invention includes minimally invasive methods to access the heart and restrain the cardiac wall, resulting in the prevention or reduction of cardiac dilation in patients known to have experienced such dilation or who have a predisposition for such dilation occurring in the future. A cardiac restraint apparatus according to the present invention is typically applied to the epicardial surface of the heart, such that the cardiac restraint apparatus at least partially enclosed the heart.
Cardiac dilation occurs with different forms of cardiac disease, including congestive heart disease, post-myocardial infarctions, and dilated cardiomyopathy. In certain instances, congestive heart disease may result from viral infections. In such cases, the heart may enlarge to such an extent that the adverse consequences of heart enlargement continue after the viral infection has passed and the disease continues its progressively debilitating course. In some cases, such as post-myocardial infarction, the dilation may be localized to only a portion of the heart. In other cases, such as hypertrophic cardiomyopathy, there is typically increased resistance to filling of the left ventricle with concomitant dilation of the left atria. In dilated cardiomyopathy, the dilation is typically of the left ventricle with resultant failure of the heart as a pump. In advanced cases, dilated cardiomyopathy involves the majority of the heart. Causes of congestive heart disease are not fully known.
As the heart enlarges, the heart is performing an increasing amount of work in order to pump blood during each heart beat. In time, the heart becomes so enlarged that the heart cannot adequately supply blood. An afflicted patient is fatigued, unable to perform even simple exerting tasks and experiences pain and discomfort. Further, as the heart enlarges, the internal heart valves cannot adequately close. This impairs the function of the valves and further reduces the heart's ability to supply blood. With each type of cardiac dilation, there are associated problems ranging from arrhythmias which arise due to the stretch of myocardial cells, to leakage of the cardiac valves due to enlargement of the valvular annulus.
Drugs are sometimes employed to assist in treating problems associated with cardiac dilation. For example, Digoxin increases the contractility of the cardiac muscle and thereby causes enhanced emptying of the dilated cardiac chambers. On the other hand, some drugs, for example, beta-blocking drugs, decrease the contractility of the heart and thus increase the likelihood of dilation. Other drugs including angiotensin-converting enzyme inhibitors such as Enalopril, which help to reduce the tendency of the heart to dilate under the increased diastolic pressure experienced when the contractility of the heart muscle decreases. Many of these drugs, however, have side effects which make them undesirable for long-term use.
Apparatus to prevent or reduce dilation and thereby reduce the consequences of dilation have also been described. Patches made from low porosity materials, for example Dacron™, have been used to support the cardiac wall. Other apparatus are found in U.S. Pat. No. 4,957,477 to Lundback dated Sep. 18, 1990; U.S. Pat. No. 5,131,905 to Grooters dated Jul. 21, 1992; U.S. Pat. No. 5,150,706 to Cox et al. dated Sep. 29, 1992; U.S. Pat. No. 5,143,082 to Kindberg et al dated Sep. 1, 1992; U.S. Pat. No. 5,256,132 to Snyders dated Oct. 26, 1993; U.S. Pat. No. 5,702,343 to Alferness dated Dec. 30, 1997; U.S. Pat. No. 6,077,218 to Alferness dated Jun. 20, 2000; U.S. Pat. No. 6,085,754 to Alferness dated Jul. 11, 2000; and U.S. Pat. No. 6,095,968 to Snyders dated Aug. 1, 2000.
The '477 patent teaches a double-walled jacket surrounding the heart. A fluid fills a chamber between the walls of the jacket. The inner wall is positioned against the heart and is pliable to move with the heart. Movement of the heart during beating displaces fluid within the jacket chamber. The '706 patent discloses a medical apparatus for enclosing an internal body organ, comprising a filamentary strand with noose and free end portions and a surgical bag with an opening. The '082 patent discloses a cooling net for cardiac or transplant surgery, comprising a porous net that is fitted and secured around the organ. Both of the '905 and '132 patents teach cardiac assist apparatus which pump fluid into chambers opposing the heart to assist systolic contractions of the heart. The '343 and '218 patents teach an adjustable jacket to constrain cardiac expansion during diastole. The '754 patent discloses a biologically compatible jacket adapted to be secured to the heart. The '968 patent discloses a viscous cardioplasty jacket for buttressing the ventricular heart walls.
None of these apparatus include a sheath to facilitate endoscopic introduction of the apparatus, or guide elements for positioning the cardiac restraint apparatus around the heart. Moreover, none of these apparatus include hollow guide tubes that permit an instrument to be advanced through their lumens to engage the mouth of the jacket and secure the mouth of the jacket to the pericardium. Furthermore, none of these references teach the introduction of a cardiac restraint apparatus via a single subxiphoid incision. Accordingly, there is a need for an improved cardiac restraint apparatus that can be more easily introduced via a minimally invasive approach, and improved minimally invasive methods for introducing cardiac restraint apparatus.